1. Field of the Invention
The invention relates to a solid-state image sensor and a method of driving the same, and more particularly to a MOS-type solid-state image sensor having a function of detecting movement, and method of driving the same.
2. Description of the Related Art
A MOS-type solid-state image sensor including a plurality of pixels each having a photoelectric converter and arranged in a two-dimensional array is sometimes designed to have a function of detecting movement. Such a MOS-type solid-state image sensor not only converts a scene detected by a sensor array, into an electric signal, but also detects movement of something in a scene detected by a sensor array, and transmits a signal accordingly. In the specification, such a MOS-type solid-state image sensor having a function of detecting movement is hereinafter called a movement-sensor.
A conventional solid-state image sensor not having a function of detecting movement is explained hereinbelow with reference to FIGS. 1 and 2.
FIG. 1 is a block diagram of a conventional MOS-type solid-state image sensor, and FIG. 2 is a circuit diagram of a pixel constituting a sensor array which is a part of the MOS-type solid-state image sensor illustrated in FIG. 1.
As illustrated in FIG. 1, a conventional MOS-type solid-state image sensor is comprised of a sensor array 801 including a plurality of pixels arranged in an array, each pixel converting a light into an electric signal in accordance with brightness of an image, a scanning circuit 802 which scans electric signals converted by the pixels, a X-scanning circuit 803 which scans the electric signals converted by the pixels, and a plurality of line memories 804 each temporarily accumulating the electric signals.
The sensor array 801 is defined by a plurality of pixels arranged in a two-dimensional array. Each of the pixels is designed to include a photoelectric transfer diode. An image projected on the sensor array 801 is converted into an electric signal by the pixels.
The Y-scanning circuit 802 transmits Y-scanning signals 807 to thereby make access to the pixels row by row in the sensor array 801 from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array 801 are concurrently read out as row signals 805.
These row signals 805 are accumulated in the line memories 804. Each of the line memories 804 is comprised of a switched capacitor, for instance. Since row signals are generally analog signals, they can be accumulated in switched capacitors by the number equal to the number of pixels existing in a row.
The X-scanning circuit 803 transmits X-scanning signals 808 to the line memories 804 to thereby make successive access to the row signals accumulated therein, and transmits an output signal 806.
As illustrated in FIG. 2, a pixel which carries out photoelectric transfer is comprised of a photodiode 901, a first n-MOSFET 902 including a gate electrically connected to a bias terminal 905, a drain electrically connected to a source voltage VDD and a source electrically connected to the photodiode 901, a second n-MOSFET 903 including a gate electrically connected to the photodiode 901, a source electrically connected to the source voltage VDD and a drain, and a third n-MOSFET 904 including a gate electrically connected to a terminal 906 through which a signal is input, a source electrically connected to the drain of the second transistor 903 and a drain electrically connected to a output line 907.
The photodiode 901 is kept biased by the first n-MOSFET 902, and hence, keeps producing photoelectric current. A bias voltage is applied to the first n-MOSFET 902 through the bias terminal 905. A voltage at the drain of the first n-MOSFET 902 is output at a low impedance through the second n-MOSFET 903.
The third n-MOSFET 904 acts as a switch. When the third n-MOSFET 904 makes access to a pixel, the third n-MOSFET 904 is turned on by the Y-scanning circuit 802 through the terminal 906. When the third n-MOSFET 902 is caused to be turned on, a pixel output signal is transmitted through the output line 907.
The conventional solid-state image sensor has such a structure as mentioned above, and operates in the above-mentioned way. If a movement sensor is designed based on the above-mentioned conventional solid-state image sensor, the movement sensor would have such a structure as mentioned below.
FIG. 3 is a block diagram of a conventional movement sensor having a structure designed based on the structure of the solid-state image sensor illustrated in FIG. 1. The movement sensor illustrated in FIG. 3 is comprised of a sensor array 1001 including a plurality of pixels arranged in a matrix array, each pixel converting a light into an electric signal in accordance with brightness of an image, a Y-scanning circuit 1002 which scans electric signals converted by the pixels, a X-scanning circuit 1003 which scans the electric signals converted by the pixels, a plurality of line memories 1004 each temporarily accumulating the electric signals, and a plurality of differential circuits 1007 electrically connected between the line memories 1004 and the X-scanning circuit 1003.
In brief, the movement sensor additionally includes the differential circuit 1007 in comparison to the solid-state image sensor illustrated in FIG. 1.
The Y-scanning circuit 1002 transmits Y-scanning signals 1009 to the sensor array 1001 to thereby make access to the pixels row by row in the sensor array 1001 from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array 1001 are concurrently read out as first row signals 1005. These first row signals 1005 are accumulated in the line memories 1004.
Then, the Y-scanning circuit 1002 makes access again to the pixel row which has been previously accessed. As a result, signals in the row are read out as second row signals 1008, which are accumulated in the line memories 1004. The line memories 1004 separately transmits the first and second row signals a 1005 and 1008 to the differential circuits 1007. The differential circuits 1007 calculates a difference between the first and second row signals 1005 and 1008. The calculation is concurrently carried out for all the first and second row signals 1005 and 1008 transmitted from a pixel row.
The movement sensor illustrated in FIG. 3 includes the differential circuits 1007 by the number equal to the number of pixels in a row in the sensor array 1001.
Output signals transmitted from the differential circuits 1007, each indicating a difference between the first and second row signals 1005 and 1008, are successively read out in accordance with X-scanning signals 1010 transmitted by the X-scanning circuit 1003. The thus read-out output signals are transmitted from the X-scanning circuit 1003 as output signals 1006.
In the above-mentioned movement sensor, since signals are read out twice from the same pixel row at a certain interval and a difference between the signals is calculated, the differential circuits 1007 transmit non-zero output signals for pixels in which a light intensity varies. When the differential circuits 1007 transmits such non-zero output signals, it is deemed that movement has occurred in the sensor array 1001.
It should be noted that the movement sensor illustrated in FIG. 3 does never spoil functions of the conventional solid-state image sensor illustrated in FIG. 1. Accordingly, the movement sensor can act as a solid-state image sensor. When the movement sensor acts as a solid-state image sensor, the Y-scanning circuit 1002 successively makes access to pixels row by row in the sensor array 1001, and signals which were read out from each of rows are output through the differential circuits 1007.
A movement sensor such as the above-mentioned one is detailed is described, for instance, in 1995 IEEE International Solid-State Circuits Conference Digest of Technical Papers, pp. 226-227, xe2x80x9cA 256xc3x97256 CMOS Active Pixel Image Sensor with Motion Detectionxe2x80x9d, A. Dickinson et al.
Apart from the above-mentioned Technical Papers, Japanese Unexamined Patent Publication No. 8-292998 has suggested an image detector including a sensor cell array which can accomplish an operation between pixels when accumulated electric charges associated with a pixel signal are read out, an amplifier, an analog-digital convertor, a scanner and a multiplexer which operate with each other to scan a designated area, and a control circuit. An area in which a target pattern exists is detected by virtue of the operation between pixels carried out by the sensor cell array. The scanner and the multiplexer randomly scans the thus detected area to thereby read out image data therefrom. Thus, only an area in which a target pattern exists is read out among all of input images, ensuring high rate at which images are processed.
Japanese Unexamined Patent Publication No. 10-313426 has suggested a solid-state image sensor having a function of detecting movement, comprised of pixels each transmitting an electric signal in accordance with an intensity of incident light, vertical signal lines each associated with each of columns of the pixels, a vertical scanning circuit which transfers electric signals transmitted from a certain row of the pixels, to the associated vertical signal line at a predetermined timing, and a horizontal scanning circuit which transfers the electric signals to horizontal signal lines. Differential circuits are arranged in the vertical signal lines. The differential circuits accumulates electric signals transmitted at a timing from the pixels as signals of the previous frame and also accumulates electric signals transmitted at the next timing from the same pixels as electric signals of the present frame. The differential circuits compare those electric signals to each other to thereby transmit output signals indicative of comparison results.
Japanese Unexamined Patent Publication No. 11-8805 has suggested a solid-state image sensor having a function of detecting movement. A plurality of pixels are arranged in a matrix. Each of columns of the pixels is electrically connected to a vertical signal line. A vertical scanning circuit selects a row, reads out signals out of the selected row of pixels, and transfers the thus read out signals to the associated vertical signal line. A signal comparison circuit and a video-signal generating circuit are positioned in each of the vertical signal lines. The signal comparison circuit accumulates electric signals transmitted at a timing from the pixels as signals of the previous frame, and also accumulates electric signals transmitted at the next timing from the same pixels as electric signals of the present frame. The signal comparison circuit compares those electric signals to each other to thereby transmit an output signal indicative of comparison result, to a shift register. The video-signal generating circuit generates a video signal in accordance with electric signals of the present frame, and transmits the video signal to a horizontal scanning circuit.
However, the movement sensors as mentioned above are accompanied with the following problems.
The first problem is that it takes about one frame period of time to detect movement. Herein, the term xe2x80x9cone frame period of timexe2x80x9d means a time necessary for the Y-scanning circuit 1002 to scan pixels from a first row to a bottom row. In other words, the term xe2x80x9cone frame period of timexe2x80x9d means a time necessary for transmitting signals defining one scene.
For instance, it is now assumed that an image varies with the lapse of time at a lower end of the sensor array 1001. This variation in an image can be first detected only when the Y-scanning circuit 1002 makes access to the pixels in a lowermost row of pixels. Since the Y-scanning circuit 1002 has made access to all rows of pixels until the Y-scanning circuit 1002 makes access to the pixels in a lowermost row of pixels, much time already passes after the variation in an image has actually occurred.
After detection of movement, an operator often desires to see a quite small area including an area in which the movement has been detected. However, it is impossible to do so by the conventional movement sensor. This is the second problem.
The third problem is that the conventional movement sensor cannot detect movement while it is operating as a solid-state image sensor, that is, not as a movement sensor, and in addition, the conventional movement sensor cannot act as a solid-state image sensor while it is in operation of detecting movement.
In view of the above-mentioned problems, it is an object of the present invention to provide a solid-state image sensor which is capable of immediately detecting movement when it has occurred, identifying an area including an area in which movement has occurred, detecting movement even while it is operating as a solid-state image sensor, and independently carrying out reading out a signal from an area in which movement has occurred and reading out signals from entire pixels in a sensor array.
In one aspect of the present invention, there is provided a solid-state image sensor including (a) a plurality of pixels arranged in a matrix in a photoelectric transfer region, A) at least one movement-detector located in the photoelectric transfer region, (c) a first Y-scanner making successive access to the pixels in rows in a predetermined region in the photoelectric transfer region, and (d) a first X-scanner reading out signals running through signal output lines extending through the predetermined region, the first and second scanners both scanning a predetermined region associated with a movement-detector which has transmitted a detection signal.
It is preferable that the solid-state image sensor includes a plurality of ovement-detectors randomly positioned in the photoelectric transfer region.
For instance, the predetermined region may be a region extensive around the movement-detector.
It is preferable that the solid-state image sensor further includes (e) a second Y-scanner making successive access to all of the pixels in rows in the photoelectric transfer region, and (f) a second X-scanner reading out signals running through all of signal output lines extending through the photoelectric transfer region.
It is preferable that the solid-state image sensor further includes (g) a first switch to which the first Y-scanner makes access, and (h) a second switch to which the second Y-scanner makes access, a first signal being read through the first switch being output to a first signal output line, and a second signal being read through the second switch being output to a second signal output line.
It is preferable that the first NY- and X-scanners operate independently of the second Y- and X-scanners.
For instance, the predetermined region may be designed to have a size defined by M pixelsxc3x97N pixel wherein M and N are integers not greater than the number of pixels defining the solid-state image sensor.
It is preferable that each of the pixels is comprised of (a1) a photodiode, (a2) a first transistor including a gate electrically connected to the photodiode, a source electrically connected to a voltage source, and a drain, and (a3) a second transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to the drain of the first transistor and, a drain electrically connected to a first output line.
It is also preferable that each of the pixels is comprised of (a1) a photodiode, (a2) a first transistor including a gate electrically connected to the photodiode, a source electrically connected to a voltage source, and a drain, (a3) a second transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to the drain of the first transistor and, a drain electrically connected to a first output line, and (a4) a third transistor including a gate electrically connected to a terminal through which a signal is input, a source electrically connected to both the drain of the first transistor and the source of the second transistor, and a drain electrically connected to a second output line, wherein when the second transistor is turned on, a pixel output is transmitted through the first output line, when the third transistor is turned on, a pixel output is transmitted through the second output line, and when both the second and third transistors are turned on, a pixel output is transmitted through both the first and second output lines.
There is further provided a solid-state image sensor including (a) a plurality of pixels arranged in a photoelectric transfer region defined by a plurality of sub-regions, (b) a plurality of movement-detectors randomly arranged in the photoelectric transfer region, each of the movement-detectors detecting movement which has occurred in the photoelectric transfer region, and transmitting a detection signal, and (c) a scanner identifying a pixel transmitting the detection signal to thereby identify a sub-region in which the movement has occurred.
For instance, the scanner may be comprised of a first Y-scanner making successive access to the pixels in rows in the photoelectric transfer region, and a first X-scanner reading out signals transmitted from the photoelectric transfer region, the first Y- and X-scanners identifying the sub-region associated with a movement-detector which has transmitted the detection signal.
It is preferable that the solid-state image sensor further includes (e) a second Y-scanner making successive access to all of the pixels in rows in the photoelectric transfer region, and (i) a second X-scanner reading out all signals transmitted from the photoelectric transfer region.
It is preferable that the solid-state image sensor further includes (g) a first switch to which the first Y-scanner makes access, and (h) a second switch to which the second Y-scanner makes access, a first signal being read through the first switch being output to a first signal output line, and a second signal being read through the second switch being output to a second signal output line.
In another aspect of the present invention, there is provided a method of driving a solid-state image sensor, including the steps of (a) transmitting a detection signal when movement has been detected in a photoelectric transfer region including a plurality of sub-regions, and (b) starting scanning a sub-region associated with a detecting circuit which has transmitted the detection signal.
It is preferable that the method further includes the step of stopping scanning the photoelectric transfer region when movement is detected while the photoelectric transfer region is being scanned in entirety, and starting scanning a sub-region associated with a detecting circuit which has detected the movement.
It is preferable that the method further includes the step of, when a second detecting circuit has transmitted a second detection signal indicating that movement had been detected in a second sub-region while a first sub-region is being scanned in response to a first detection signal transmitted by a first detecting circuit, indicating that movement had been detected in the first sub-region, starting scanning the second sub-region after the first sub-region has been completed to be scanned.
It is preferable that the method further includes the step of, when a second detecting circuit has transmitted a second detection signal indicating that movement had been detected in a second sub-region while a first sub-region is being scanned in response to a first detection signal transmitted by a first detecting circuit, indicating that movement had been detected in the first sub-region, immediately starting scanning the second sub-region, if the first and second sub-regions do not have common row and column.
It is preferable that when movements have been detected in a plurality of sub-regions, the sub-regions are scanned in accordance with a predetermined order.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
In the solid-state image sensor in accordance with the present invention, a plurality of the movement-detectors are randomly arranged in a photoelectric transfer region independently of the pixels. The movement-detectors detect movement having occurred in a photoelectric transfer region regardless of whether the solid-state image sensor acts as an ordinary solid-state image sensor or a movement sensor. A detection signal transmitted by the movement-detectors when they detect movement in a photoelectric transfer region is immediately transmitted to the first X- and scanning circuits, which in response scan a pixel identified by the detection signal. Hence, the solid-state image sensor makes it possible to detect movement independently of a frame period, ensuring reduction in a time necessary for detecting movement in comparison with a conventional solid-state image sensor.
In addition, the solid-state image sensor in accordance with the present invention can detect movement while it operates as an ordinary solid-state image sensor, that is, it scans a photoelectric transfer region in entirety.
In accordance with the solid-state image sensor, it is possible to pick up images associated with a region in which movement has been detected, by means of the first X- and Y-scanning circuits.
Furthermore, by designing each one of the pixels to include two switches to each of which the first and second Y-scanning circuits make access. and designing the pixel to transmit output signals to separate output signal lines, the solid-state image sensor can scan a photoelectric transfer region in entirety and scan a sub-region in which movement has been detected, at the same time.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.